This invention relates to a method for manufacturing a multi purpose building material from various waste materials. The invention also relates to a production plant for performing the method, products obtainable by the method, uses of the products and a method for the disposal of waste materials, especially the disposal of used tyres, in particular those made of rubber or synthetic rubber.

The costs of disposing of domestic and industrial waste continue to increase, due to increases in the amount of waste products produced and the lack of landfills and other means for disposing of waste. In view of this, as well as the increase in pressure to dispose of waste in ways less harmful to the environment, a number of methods for recycling waste have been proposed.

Previous methods for recycling waste require the waste to be separated into specific waste types, such as glass, plastic, metal, cardboard and the like. Separating waste is time consuming, labour intensive and expensive. Furthermore, waste separation has to be done accurately. If for example, plastics material is separated from mixed waste for recycling and the separated plastics material is contaminated by a single piece of glass, major problems in recycling and possible damage to the recycling apparatus can occur.

Previous methods for recycling waste in addition to requiring the waste to be separated, generally, require the separated waste to be clean. This is a major problem as waste is generally dirty and cleaning procedures are expensive, time consuming and can cause further damage to the environment through the use of detergents and other cleaning products.

One type of waste material which is particularly desirable

to recycle is plastics material.

Plastics material is used more and more in goods and packaging and is extremely difficult to degrade, thereby posing a major problem to the environment. A number of methods have previously been described for recycling plastics material.

Generally, the previous methods for recycling plastics material require that the plastics material is not only separated from other waste types but also the specific types of plastics material are separated from each other. For example, high density polyethylene, low density polyethylene and polypropylene are separated from plastics materials such as polyvinyl chloride, polyester and polystyrene as described in EP-A-0568710. Alternatively, the percentages of the different types of plastics have to be controlled, as described in WO 92/15640, wherein at least 80% of the plastics material is comprised of compounds such as high density polyethylene, low density polyethylene, homopolymers of polypropylene, copolymers of ethylene and propylene, and combinations thereof. The remaining 20% of the plastics material is made up of polymeric materials such as rigid or flexible polyvinyl chloride, polystyrene, polyamides and polycarbonates or combinations thereof.

Generally, previous processes for recycling plastics material comprise the steps of melting the separated and washed plastics materials in an extruder and extruding the plastics composition. The extrudate is then forced into a series of molds and cooled.

The major disadvantages of the previous recycling methods include the need to separate and wash the plastics materials. Previous methods are therefore labour intensive, time consuming and expensive. Furthermore, the extrusion step of previous methods leads to a slow rate of production, approximately two tons a day.

The present invention overcomes the problems and deficiencies of the previous methods for recycling waste material as there is no need to separate the waste and no need to clean the waste material. Furthermore, the present invention has a rate of production of approximately 50 tons an hour and is therefore substantially more efficient.

The product obtained by the method herein described is substantially uniform in its composition and density and can be worked using conventional techniques and tools. The product can be formed into different shapes and forms depending on the required use of the material. Furthermore, contaminated articles such as sharps from hospitals, shot blast contaminated with lead paint, contaminated articles from chemical industries and the like, can be incorporated into the mix where they are encased within the final product and thereby made safe.

Amongst the most difficult waste products to dispose of are used tyres, from the smallest tyres for bicycle wheels to the largest tyres used on earth working machines. Although there are some recycling methods for tyres in existence, such as using them for playground surfaces for example, there are insufficient outlets for utilising the end product and as a result they are usually disposed of in the same way as other waste products, ie. in landfills, and it is usual, before disposing of them, to shred them.

Many millions of used tyres are disposed of each year in each country, and worldwide the number of used tyres to be disposed of runs into billions. The cost of transporting, shredding and burying the tyres is enormous, and a constant problem for the authorities charged with disposing of these products has been to find a cheap and effective way of removing them from the environment. The present invention seeks to provide a solution to this problem.

The present invention provides a method for manufacturing a multi-purpose building material from domestic and/or industrial waste material comprising providing waste material having a plastics material content between 20% and 65% by weight, shearing the waste material to particles of at most about 50mm in diameter, charging the particulate waste and a particulate filler to a mixer, heating and maintaining the temperature of the mixture between 120°C and 200°C during mixing and mixing until a uniform composition is obtained, and forming the uniform composition into a final product.

The domestic waste and/or industrial waste used can contain any material including glass, metal, cardboard, paper, cloth, masonry and foodstuffs. Preferably, the amount of waste material incorporated into the final product is in the range of 30% to 70% by weight. However, the exact amounts incorporated will depend on the type of waste material used and the desired properties of the final product. The minimum of 20% plastics material may be an integral part of a waste material or at least part can be specifically added to the waste material. In this context, the term plastics material comprises all plastics including thermoplastic, thermosetting, high density and low density plastics, e.g. polystyrene, polyvinyl chloride and polypropylene. The plastics material does not need to be cleaned and a mixture of plastics can be added. Preferably, the amount of plastics present in the final product is between 27% and 60% by weight. More preferably, the amount of plastics present in the final product is about 30% by weight. However, the amount of plastics present in the final product will vary depending upon the desired properties of the final product. For example, if the product is required to float in water, the final product must contain greater than about 50% plastics material.

The particulate filler can be any friable material such as calcium carbonate, asbestos, mica, wollastonite, talc.

diatomaceous earth, kaolin clays and carbon filaments. Preferably, the particulate filler is a waste product from another process; such products include fly ash, sand fines, core sand, flue dust, shot blast and alumina dust. A single filler or a combination of fillers can be added and furthermore, contaminated fillers such as shot blast contaminated with lead paint may be used. Preferably, two different particulate fillers are added. More preferably, the particulate filler consists of fly ash and minor additions of either core sand and/or shot blast.

The amount of particulate filler added depends upon the desired properties of the final product being obtained. Preferably, the particulate filler is present in an amount between 30% and 70% by weight of the final product. In a further embodiment of the present invention, the components are dried and/or heated, before entering the mixer. Preferably, the compounds are heated to between 120°C and 200°c before entering the mixer.

Preferably, the waste material and particulate filler are fed into the mixer at equal rates, so that uniform mixing occurs. More preferably, the waste material and particulate filler are fed into the mixer at equal rates by screw or air conveyance.

Mixing occurs at a temperature in the range of 120°C to 200°C, preferably in the range of 150*C to 190 ^β C and, more preferably, at a temperature of about 160°C. However, the exact temperature during mixing will depend on the desired characteristics of the final product.

By limiting the maximum temperature during mixing to 200°C, production of toxic emission from the waste material is eliminated. This is a further advantage over the previous methods of recycling.

An alternative embodiment of the present invention further

comprises the additional step of keeping the uniform composition indefinitely at temperatures as low as 120°C, prior to use, in a holding tank.

The uniform mixture can be formed into any desirable shape. Preferably, the heated mixture is rolled or molded into the desired shape by conventional methods. More preferably, the heated mixture is pressed into a mold at high pressure, preferably at 281 kg/cm ² for about seven days. The exact molding and forming conditions will vary depending upon the type of product being produced.

The products obtained by the method of this invention are resistant to degradation, will not rot, are resistant to acidic and alkaline conditions, heat resistant, soundproof, extremely strong and have a maximum porosity value of 0.81%.

The product can be worked using conventional techniques and tools and furthermore the product itself can always be recycled by repeating the method herein disclosed.

The product can be used for any type of building or construction purpose. For example, the product can be used as building blocks, foundations for buildings (the product would also have the added advantage of eliminating the need for damp courses, due to its low porosity value), roof tiles, fence posts and panels, paving slabs and tiles, water gulleys, playground surfaces, roads and paths, pipes (especially sewage pipes) , pushing walls and floors for waste transfer stations, floors for car parks and garage forecourts, groins for land and beach reclamation, tetropods and acropods for coastal defences and blocks for sea walls and marine walls. The product can also be used as a membrane for landfills and other similar purposes.

In a further embodiment of the present invention, a number of additives can be included in the product depending on the ultimate use of the final product, such as ultraviolet light

absorbers, anti-fungal agents, fire retardants, heat insulators, colouring agents,.. impact modifiers and reinforcing agents (such as chopped strands of glass fibers) , viscosity stabilizers and various processing aids.

In another further embodiment of the present invention, contaminating matter such as hospital waste (including sharps) , contaminated matter from chemical industries and the like can be incorporated into the product.

Any contaminated components will become coated and encapsulated by the plastics component of the mixture. As the plastics component melts it envelops and forms a coat around the non-plastics components of the mix. Furthermore, in the preferred forming step, the plastics component is differentially distributed on the external surfaces of a molded article. Thus, the non-plastic components are encased within the interior of the article, thereby sealing them from the external environment.

In a further embodiment, additional plastics material can be added to the mixture during mixing. The addition of plastics material at this point in the process can lead to a development of a mottled or marble appearance on the surface of the final product. Preferably, the additional plastics material is in the form of plastic sheeting or similar material.

A further embodiment of the present invention is the introduction of the uniform composition produced by the method of the present invention into a tyre to be disposed of. The uniform composition is allowed to solidify therein so as to form a solid disc bounded by the said tyre. The product, which is effectively a used tyre containing a solid disc of waste material, may then be disposed of in the usual way, eg. in landfills, or they may be used as or in the production of articles of construction. When disposed of in landfills, they may be arranged in layers.

and this represents a most efficient way of disposing of them, particularly if the voids between the peripheries of the tyres are filled with further waste material, eg. waste which has been treated to form a uniform composition as described hereinabove.

Their use as or in the formation of construction materials represents an efficient method of recycling both the unused tyres and domestic and/or industrial waste material. For example, the products may be superposed to form a stack, which may suitably be encased in a steel tube to form a building column or pile. Such would be of particular application in building construction, eg. as foundations or columns, and in the construction of sea walls and marine walls.

An alternative method for forming a column comprises superposing a plurality of tyres for disposal, one on another, pouring uniform composition made from waste material as described hereinabove into the central hollow formed by the superposed tyres, until the tyres are filled with the composition, and allowing the composition to set, if desired under pressure. Such a method will provide an extremely strong column, suitable for many building applications.

The present invention also relates to a production plant, for performing the methods disclosed herein, comprising means for storing the product components, heating and mixing means, means for feeding the components to the heating and mixing means and means for forming a final product. In a preferred embodiment, means for weighing the components and means for drying the components are also included within the production plant.

Specific embodiments of the process, products and production plant according to the present invention, will now be described further, by way of example, with reference to the

accompanying drawing in which:

FIGURE 1 illustrates schematically a production plant for. performing the claimed method;

FIGURE 2 is a diagrammatic view of a used tyre being filled with composition;

FIGURE 3 is a diagrammatic plan view of a land fill, showing the floor covered with treated tyres; and

FIGURE 4 is a diagrammatic view of the production of a column from used tyres.

Example

Production of twenty ton blocks for use as sea walls

Twenty ton sea walls are produced using the apparatus illustrated in Figure 1, wherein the various materials necessary for forming the final product are stored in a number of storage silos (1, 2, 3). The various materials are fed into weigh vessels (7, 8) by screw conveyors (4, 5, 6) . The various materials are weighed and preferentially distributed between a rotary drier (11) and a mixer (12) by screw conveyors (9, 10). The various components which are fed into the rotary drier (11) are subsequently fed to the mixer (12) by a screw conveyor (13) . The various components are mixed in the mixer (12) and then the uniform mixture obtained is fed via a screw conveyor (14) into twenty ton molds (15). The twenty ton molds are pressed at pressures of 281 kg/cm ² for seven days. The final product can be easily removed from the molds (15) .

Referring to Figure 2, there is shown a tyre (101), to be disposed of, into which is being introduced, from a hopper (102) , heated uniform composition produced from waste material by the method of the present invention. The

composition (103), suitably at a temperature of 120°C or more, flows into the annulus formed b the tyre (101) and also fills up the central part of the tyre to form, on setting off, a disc of waste material bounded by the tyre (101) .

Such products may be disposed of in landfills such as the land fill (110) shown in plan in Figure 3. Such would conventionally comprise a large crater (111) into which, conventionally, would be charged domestic or industrial waste material. As shown, disc products (112) , such as that shown in Figure 2, are laid on the floor of the land fill, suitably in layers one on the other, and this represents an efficient way of disposing of both the used tyres and other waste material. Further waste material, suitably treated according to the method of the present invention, may be charged into the void spaces (113) .

In the production of construction articles, eg. piles or columns, products produced as shown in Figure 2 may be superposed one on the other, and if desired encased in steel or other tubes. Alternatively, columns may be formed as illustrated in Figure 4. As shown in Figure 4, a plurality of used tyres (120) are superposed, and heated uniform composition prepared as above is introduced into the central hollow space formed by the superposed tyres by way of a hopper (121) . The composition (122) continues to be poured into the stack of tyres (120) until the stack is completely filled with composition (122) . Pressure may be applied for this purpose. When the composition has set off, a rigid and strong column (123) , suitable for constructional purposes, is obtained.

The above embodiments have been described by way of illustration only. Many other processes, products and uses of the products will be apparent to one skilled in the art. Furthermore, various modifications, additions or substitutions may be made without departing from the scope

of the present invention, as according to the accompanying claims.